So, you flushed your toilet and in addition to the normal flushing sounds you expect, you also hear a faint gurgling coming from your bathtub drain.
What the heck is that?
You flush the toilet again and listen closely. Sure enough, the gurgling sound happens again. What could it be?
If you are here, I am assuming you are experiencing this issue. Rest assured, there is no cause for panic. While you do need to get to the root of the problem, the chances of something major happening are slim as long as you don’t ignore the issue. In many cases, you will be able to resolve the issue yourself, but if you find the cause to be something more involved, you will need to call in a plumber.
In the article below, I am going to tell you why your bathtub gurgles when you flush the toilet and what you can do to fix it.
Why Your Bathtub Gurgles When The Toilet Is Flushed
Essentially, the gurgling sounds you hear coming from your bathtub drain when you flush the toilet are pressure changes in the pipelines as air flows into and out of the sewer system. Since all the drains in your home leave via the same route, if one drain is affected, they all (or at least the ones closest to the problematic drain) will be as well. Let’s take a look at some of the reasons pressure changes happen in a home’s plumbing.
P-Trap Water Level
Most bathtub drains have what is called a P-trap. The P-trap’s job is to keep a certain amount of water in the pipe to prevent the passage of air. If your bathtub lacks a P-trap, air could be escaping from the bathtub drain every time the toilet is flushed, thus the gurgling sound as air passes through any water that remains in the drain.
Blocked Air Vents
Every home plumbing system is ventilated through the roof. This ventilation system is important as it allows sewer gases and excess air in the sewer system to escape up and out of your home so that it doesn’t come inside. If something blocks this vent, it will prevent air from passing partially or completely, which can result in gurgling in the drains of your home.
Air Dispersion from Drains
Air in your home’s plumbing system is normal, and this is why the ventilation system is so important. If the vent is blocked or closed in any way, the air in the pipes must go somewhere when the water is running (i.e., when the toilet is flushed). If the air cannot escape through the ventilation system, it will make its way through the first available drain along the pipeline, which very well could be your bathtub drain.
How to Prevent The Bathtub Drain Gurgling
As I mentioned earlier, you may be able to resolve the annoying gurgling sound in your bathtub without the aid of a trained plumber. Read on for some solutions that may work for you.
Plunge The Toilet To Clear Pipeline
A quick and easy solution to the gurgling sound in your shower, when you flush the toilet, is to plunge the toilet. There may be trapped air or an obstruction in the pipeline that once removed, will stop the gurgling noises.
To use this method, get some duct tape and a flange plunger. Begin by taping all the drains and overflow drains shut. Make sure the tape is adhered securely so that it creates a watertight seal. All drains in the bathroom except the toilet should be covered with duct tape.
Use your flange plunger to plunge the toilet. Make sure that water covers the head of the plunger completely and vigorously move the plunger up and down to dislodge any debris in the pipes and coax any trapped air along. You may need to plunge the toilet for several minutes or multiple times to fully clear the pipes. Once you are done plunging, try flushing the toilet and listen for the gurgling sounds. If you still hear them, try plunging the toilet again.
Check The Ventilation System is Clear
Your home’s plumbing ventilation system must be clear at all times for its drains to drain properly. It is not uncommon for leaves and/or other debris to collect in these vents, causing a blockage that hinders the proper operation of the sewer system. Sometimes, birds and other small animals get inside these vents and build nests, too.
If you discover this to be the cause of the gurgling in your bathtub, I recommend calling in a plumber to clear the blockage. In most residential dwellings, the sewer vent is located on the roof, which can be a dangerous place to be if you don’t know what you are doing.
That said, if you want to attempt to clear the vent yourself, you can do so using a garden hose to flush the debris out or a snake auger if it is long enough to reach the blockage. If you are lucky and your home’s sewer vent has a screen covering it, you may just need to remove any debris that is clogging the screen to resolve the issue.
The Pipeline May Be Too Narrow
This is a rare occurrence, but in some instances, the pipes that carry waste away can be too narrow to accommodate things that are flushed. For example, if you use large amounts of toilet paper, flush things that shouldn’t be flushed, or eat a high-fiber diet that results in excessive bowel movements, the drain leading away from your toilet may become clogged. When this happens, the blockage may cause a gurgling sound in your bathtub as air struggles to travel past the clog.
If this is a chronic issue, you may need to replace the small pipes with larger ones. While this isn’t an expensive fix, it can be quite messy and challenging, especially if you don’t have any plumbing experience. Again, I recommend calling in a plumber to advise you on this one as there may be a better, less daunting solution.
Blocked Sewer Lines
Blocked sewer lines rarely result in gurgling sounds coming from a home’s drains, but in theory, it can happen, which is why I’m including it in this post. Blocked sewer lines can be a major pain, both in cost and stress. If there is a blockage in your home’s sewer lines, the fix is usually more complicated than simply switching out pipes or plunging the toilet. You will need to call a plumber to clear the lines.
Use a Chemical Cleaner in the Bathtub Drain
If you suspect a clog to be the culprit of the gurgling sound coming from the bathtub when you flush the toilet, you can attempt to dislodge or dissolve it using either a homemade drain cleaner or a store-bought drain cleaner. In most cases, you will want to pour the drain cleaner into the toilet, but you can also use it in the bathtub drain as well.
For the homemade drain cleaner, you need baking soda, white vinegar, and a gallon of hot water. Pour a good amount of baking soda into the toilet, followed by a good amount of vinegar. The combination of these two ingredients will create an effervescent reaction that can dissolve organic materials.
Allow the mixture to do its thing for 20 minutes or so and then pour the hot water in. Pour the water from the waist level to create enough force to push the blockage along.
If the blockage is a stubborn one, the homemade concoction may not be powerful enough to clear it. In this case, you can purchase a commercial drain cleaner for the job. You can purchase cleaners such as Liquid-Plumr and Drano from Amazon.com and both will clear stubborn clogs in all types of drains.
When To Call A Plumber
Plumbing issues can be tricky to resolve, especially if you don’t have any experience or understanding of how your home’s sewer system works. If you try the methods listed above and nothing seems to resolve your gurgling bathtub issue, you may need to call in the big guns. A plumber will be able to inspect your home’s sewer system, diagnose the issue quickly, and get it fixed for you once and for all.
When your bathtub gurgles when the toilet is flushed, it can be a frustrating and annoying issue. While the noise seems harmless, it can be an indication of something more serious going on with your home’s sewer system. If, after trying to resolve the issue you and your bathtub still gurgle with each flush, contact a plumbing professional immediately.
As a retired Master Plumber Jamie has over 30 years of hands-on experience, making his plumbing knowledge second to none. He has also worked on both residential and commercial HVAC installation and repair projects.